The present disclosure is directed to a position sensor of an actuator, such as a control valve. The control valve can be of a process engineering plant, for example a chemical plant, such as a petrochemical plant, a power plant, a food processing plant such as a brewery, or the like. The present disclosure relates to an actuator with a position sensor. The actuator can be, for example, a regulator valve, a control valve or a shut-off valve, such as an emergency shut-off valve, but is not limited thereto.
A position sensor is described, for example, in German Patent Application Publication No. DE 38 44 020 A1. This position sensor can detect a rectilinear motion of a drive rod of an actuator, such as a control valve, in order to report it to a central monitoring station. According to DE 38 44 020 A1 A, linear or angular movement can be detected by way of an amplitude or resistance change as a result of a core and slider moving relative to each other, or by a Hall-effect sensor, a capacitive sensor, a rotary encoder or a rotary potentiometer. In the known system, a linear conversion of the distance into an electrical measurement variable is performed. In the specific design in accordance with DE 38 44 020 A1, the position sensor detects a linear valve-rod distance via a lever which is connected to a measuring shaft in a rotationally fixed manner, and causes a corresponding rotational movement of the measuring shaft. The shaft has a sectionally semi-circular cross-section, on the flat side of which a Hall-effect sensor is mounted, which rotates between two stationary magnetic poles fixed to the housing of the position controller. With the Hall-effect sensor, the actual angular position of the measuring shaft relative to the housing can be detected. In the position controller described in DE 38 44 020 A1, it has been found that the achievable measuring accuracy is limited due to production, assembly and mounting tolerances. With the known position sensor, the real actual angular position of the measuring shaft and the actual position of the actuator, derived therefrom, can only be determined with relatively low accuracy. It has also proved to be disadvantageous that due to the movement of the shaft, the wiring of the shaft-mounted Hall-effect sensor is subject to adverse levels of wear. This is particularly problematic for safety-critical actuators, such as emergency shut-off valves.
U.S. Patent Application Publication No. 2003/0086470 A1 describes a position sensor for an actuator, in which the control path of a valve control rod is taken via a lever and transmitted to a measuring shaft. Two magnets are arranged on the measuring shaft, which are mounted on the housing of the position sensor at a fixed position at the height of the axis of rotation of the measuring shaft. Because of the positionally fixed arrangement of the magneto-resistive sensor element, wear on the sensor cabling is avoided. However, with US 2003/0086470 A1, the position sensor production, assembly and mounting tolerances also occur, and consequently measurement errors also occur. In addition, sometimes transient or abrupt actuator movements, for example when rapidly switched off, have a detrimental effect on the magnetization of the permanent magnets. Therefore, for detecting an actual angular position for safety-critical actuators, such as emergency shut-off valves, the position sensor in accordance with US 2003/0086470 A1 has only limited suitability.
A further position sensor is described from German Patent Utility Model No. DE 200 08 930 U1, in which a measuring shaft can sense a linear motion of an actuator with a control valve via a lever. A permanent magnet is attached to the end face of the measuring shaft, the rotational movement of which is detected by a GMR sensor fixed to the housing. As a result of assembly tolerances, manufacturing tolerances and/or mounting tolerances of the measuring shaft, measurement errors can also occur with this sensor. The position sensor known from DE 200 08 930 U1 is therefore also rather unsuitable for safety-critical applications of actuators, such as emergency shut-off valves.
The exemplary embodiments of the present disclosure will be described with reference to the accompanying drawings. In the drawings, the same or similar components are referenced with the same or similar reference numerals.